SSC-JUNIOR ENGINEER (Civil & Structural) Online Exam 2016 (Part-II)

Total Questions: 50

11. The strain energy stored in a body due to external loading, within the elastic limit is known as ___________.

Correct Answer: D. resilience
Solution:Resilience is the total energy stored in a body within the elastic limit. When the external forces are removed from a strained body, the body starts doing work. Keeping this in view, resilience is also defined as the capacity of a strained body for doing work on the removal of the forces which caused the strain.

Proof resilience is the maximum strain energy stored in a body. The strain energy is maximum when a body is strained up to its elastic limit. Thus, proof resilience can also be defined as the quantity of strain energy stored in a body when strained up to its elastic limit.

Modulus of resilience is the greatest amount of strain energy per unit volume that a material can absorb without exceeding the elastic limit. That is,

Modulus of resilience = Proof resilience/Volume of the body.

12. The area under stress strain curve represents __________.

Correct Answer: B. toughness of material
Solution:Toughness Expressed as Area under the Stress-Strain Curve: One simple way of describing toughness is to consider it as the total area under the stress-strain curve. This area is indicative of the amount of work done per unit volume, a quantity that comprises both strength and ductility.

13. The partial factor of safety for concrete as per IS 456-2000 is _________.

Correct Answer: A. 1.5
Solution:According to IS Code (IS 456 : 2000) for design purposes the compressive strength of concrete in the structure shall be assumed to be 0.67 times the characteristic strength of concrete in cube and the partial safety factor Yₘ꜀ = 1.5 shall be applied in addition to this.

14. Approximate ratio of the strength of the cement concrete of 7 days to that of 28 days is __________.

Correct Answer: A. 0.56
Solution:No explanation given in the book

15. Durability of concrete is proportional to _________.

Correct Answer: D. cement-aggregate ratio
Solution:The durability of concrete is its resistance to the aggressive environmental conditions. High strength concrete is generally more durable than low strength concrete. In situations when the high strength is not necessary but the conditions of exposure are such that high durability is vital, the durability requirement will determine the water-cement ratio to be used.

The water-cement ratio is a fundamental factor controlling durability because it determines the permeability of cement-paste and, therefore, to a large extent of concrete. The strength is not an adequate means of ensuring durability because it depends not only on the water-cement ratio but also on the cement properties.

When the concrete is subjected to chemical attack a suitable type of cement or admixture has to be used, this has to be accounted in the design. If the air entrainment is used to enhance the durability. it has to be taken into account in the mix design. Thus strength, type of cement and admixture, and durability determine between them the water-cement ratio required.

16. The Young's modulus of concrete (Ec) is given by __________.

Correct Answer: B. 5000 √f꜀ₖ
Solution:No explanation given in the book

17. Low temperature during concrete laying _________.

Correct Answer: A. increases strength
Solution:Modular Ratio: Short term modular ratio is the modulus of elasticity of steel to the modulus of elasticity of concrete.

Short-term modular ratio = Es/Ec
Es = modulus of elasticity of steel (2 × 10⁵ N/mm²)
Ec modulus of elasticity of concrete (5000 × SQRT (f꜀ₖ) N/mm²)

As the modulus of elasticity of concrete changes with time, age at loading, etc., the modular ratio also changes accordingly. Taking into account the effects of creep and shrinkage partially IS code gives the following expression for the long term modular ratio. Long term modular ratio.

Long term modular ratio (m) = 280/(3f꜀ₚ꜀)
Where, f꜀ₚ꜀ = permissible compressive stress due to bending in concrete in N/mm².

18. Water cement ratio is generally expressed in volume of water required per __________.

Correct Answer: C. 30 kg
Solution:The aggragate-cement ratio is the ratio of the weight of water to the weight of cement used in a concrete mix. A lower ratio leads to higher strength and durability, but may make the mix difficult to work with and form. Workability can be resolved with the use of plasticizers or super-plasticizers.

19. The entrained air in concrete ________.

Correct Answer: A. increases workability
Solution:Workability of concrete increases with increase in water content. The higher the water content per cubic metre of concrete, the higher will be the fluidity of concrete, which is one of the important factors affecting workability.

Adding more water to concrete also has some disadvantages as given below.

Increased quantity of water may cause bleeding in concrete.

Cement slurry also escapes through the joints of formwork.

Strength of concrete may be reduced.

20. Poisson's ratio for concrete _________.

Correct Answer: A. increases with richer mix
Solution:Poisson's ratio is the ratio between lateral strains and longitudinal strains. Poisson's ratio varies between 0.1 for high strength concrete and 0.2 for weak mixes. It is normally taken as 0.15 for strength design and 0.2 for service ability criteria. Poisson's ratio for concrete increases with richer mix.